The present invention relates to wireless communication devices, and more particularly to clock circuits within wireless communication devices.
The use of wireless communication systems continues to expand. Wireless devices allow a user to communicate voice or data to other devices and people without having to remain in a fixed location. This allows users to, for example, move freely about the community while talking on the phone. The price for the convenience of using wireless devices is the addition of one more item to our already cluttered pockets and purses. To reduce the impact of wireless devices on our pockets, consumers have demanded smaller, lighter, less expensive devices that include more features such as programmable alarms and automated power control.
To implement automated and programmable functions, a real time clock within the wireless device is generally required. The real time clock provides a precise representation of time which can be compared to stored values in registers to provide automated functions. During power interruptions, the real time clock is typically powered from either a dedicated clock battery, such as a small button cell, or from a storage capacitor. If power interruptions are expected to be relatively long, then a dedicated clock battery is used. If on the other hand the power interruption is expected to be relatively short, such as upwards of 30 seconds for a battery change operation, then a storage capacitor is used. In both cases, the backup power source, battery or storage capacitor, adds weight and uses additional space, thereby increasing the size and weight of the wireless device. Since the backup power source must supply all of the power for the real time clock during the power interuption, the size of the backup power source is directly related to the power that is drawn by the real time clock during the power interruption. Universally, conventional circuits in both cases continue to maintain accurate time during the power interruption. After all, a real time clock is supposed to provide the real time. However, maintaining accurate time places a greater power load on the backup power source, necessitating a larger battery or storage capacitor. What is needed is a system to reduce the power consumed by the real time clock circuit during a power interuption so that a smaller, lighter backup power source may be used. A smaller, lighter backup source translates to a smaller, lighter wireless device.
The present real-time clock circuit saves real time information during removal of a battery. The battery provides power to the clock circuit during a steady-state mode. The clock circuit includes an oscillator assembly for generating a periodic waveform. A counter accumulates real time information in response to the periodic waveform. An energy storage device is coupled to the counter to supply energy to the counter while the battery is removed. A switch is coupled between the battery and the energy storage device to prevent the energy storage device from supplying energy to components other than the counter during removal of the battery. The switch provides a path for energy to flow from the battery to the energy storage device, thereby charging the energy storage device.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.